Visual distance cues modulate neuromagnetic auditory N1m responses

Objective: Auditory distance judgment relies on several acoustic cues and can be modulated by visual information. Sound intensity serves as one such cue as it decreases with increasing distance. In this magnetoencephalography (MEG) experiment, we tested whether N1m MEG responses, previously described to scale with sound intensity, are modulated by visual distance cues. Methods: We recorded behavioral and MEG data from 15 healthy normal hearing participants. Noise bursts at different sound pressure levels were paired with synchronous visual cues at different distances. We hypothesized that noise paired with far visual cues will be represented louder and result in increased N1m amplitudes compared to a pairing with close visual cues. This might be based on a compensation of visually induced distance when processing loudness. Results: Psychophysically, we observed no significant modulation of loudness judgments by visual cues. However, N1m MEG responses at about 100 ms after stimulus onset were significantly stronger with distal compared to proximal visual cues in the left auditory cortex. Conclusions: Our results suggest an audio-visual interaction at an early stage in the left auditory cortex, possibly related to cue integration for auditory distance processing. Significance: Sound distance processing could prove itself as a promising model system for the investigation of intra-modal and cross-modal integration principles. (C) 2012 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.